Full duplex wideband communications system for a local coaxial network

ABSTRACT

Systems and methods are disclosed for a full duplex wideband communications system for a local (e.g. in-home) coaxial network. The system employs a Frequency-division duplex (FDD) scheme that allows identical wideband modems to communicate with each other. To achieve this, the wideband modems contain a duplexer and a switch that allows reversing the connection of the wideband transmitter and receiver to the duplexer. Each wideband modem includes a control modem that is used to control access to the wideband channels. A wideband transmitter, which may be included in a modem associated with a server set-top terminal (STT), transmits a video presentation to a wideband receiver, which may be included in a modem associated with a client STT.

RELATED APPLICATIONS

This patent application is a continuation-in-part of copending U.S.patent application Ser. No. 10/342,670 filed Jan. 15, 2003.

FIELD OF THE INVENTION

This invention relates in general to broadband communications systems,and more particularly, to the field of a full duplex widebandcommunications system operating within a local coaxial network.

DESCRIPTION OF THE RELATED ART

Subscriber premises receiving cable television or satellite servicetypically have a coaxial network for providing received signals tovarious rooms in the premises. The coaxial network typically connectsset-top terminals (STT) for decoding the signals (e.g., cable orsatellite television (CATV) signals) to a communications system. It willbe appreciated that other equipment, such as cable modems and videorecorders, to name a couple, can also be connected to the coaxialnetwork. The transmitted signals may be, therefore, video/audio signal,telephony signals, or data signals.

Traditionally, an individual STT could not communicate with the othernetworked STTs; they were receiving devices that may have had thecapability to transmit data to a headend facility in the system. Astechnology progressed, a server STT could communicate with a pluralityof remote STTs in a network. This communication is desirable in that theserver STT could share files or programs with the remote STTs uponcommand from the remote STT. By way of example, the server STT maycontain storage media, such as hard disk drives, to store videoprograms. Accordingly, the networked remote STTs may want to view thosestored programs. In this manner, upon request, the server STT cantransmit a program to the requesting remote STT for viewing at that STT.Further information regarding a networked multimedia system thatincludes a server and remote STTs can be found in copending U.S. patentapplication Ser. No. 10/342,670 filed Jan. 15, 2003, the disclosure andteachings of which are hereby incorporated by reference.

A need exists, however, for systems and methods that improve uponcommunications among networked equipment in a subscriber premises.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the followingdrawings. The components in the drawings are not necessarily drawn toscale, emphasis instead being placed upon clearly illustrating theprinciples of the invention. In the drawings, like reference numeralsdesignate corresponding parts throughout the several views.

FIG. 1 illustrates a block diagram of a coaxial network 100 thatincludes a plurality of STTs for receiving and decoding CATV signals.

FIG. 2 illustrates a block diagram of two networked modems and afrequency range plan that are suitable for employing the full duplexwideband communications in accordance with the present invention.

FIG. 3 illustrates a simplified block diagram of the RF portion of aset-top terminal.

FIG. 4 illustrates a simplified STT including a wideband modem inaccordance with the present invention.

FIG. 5 is a graph illustrating a frequency response of a wideband modemin a coaxial network having a multipath environment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the invention can be understood in the contextof a broadband communications system and a local network. Note, however,that the invention may be embodied in many different forms and shouldnot be construed as limited to the embodiments set forth herein. Forexample, transmitted broadband signals include at least one ofvideo/audio, telephony, data, or Internet Protocol (IP) signals, to namebut a few. Devices included in the broadband communications system forreceiving the transmitted broadband signals may include a set-topterminal (STT), a television, a consumer electronics device such as aDVD player/recorder, a computer, a personal digital assistant (PDA), orother type of electronics device. Furthermore, in accordance with thepresent invention all of these receiving devices may include a modem orbe connected to a stand-alone modem for receiving high speed data. Allexamples given herein, therefore, are intended to be non-limiting andare provided in order to help clarify the description of the invention.

The present invention is directed towards a full duplex widebandcommunications device and system that are suitable for use in a coaxialnetwork. The coaxial network is typically confined to a subscriberpremises. It will be appreciated, however, that the network can also beused in a multi-unit dwelling, business, school, hotel, or hospital,among others. Advantageously, the present invention allows for fullduplex wideband communications among STTs or modems that are connectedin the coaxial network. The communications between any pair of STTs(e.g., a server STT and a remote STT or two remote STTs) are at datarates suitable for high definition video transmissions. The presentinvention also allows multiple STTs to share the network withoutinterference with each other. Additionally, a STT, for example, theserver STT, is capable of providing different content to differentremote STTs concurrently. Furthermore, the communication between STTsand the reception of conventional CATV signals occur simultaneouslywithout interference to the received CATV signals. As mentioned, themodem can be a standalone device that is connected to an STT and stillutilize the full duplex wideband communications in accordance with thepresent invention.

FIG. 1 illustrates a block diagram of a coaxial network 100 thatincludes coaxial cables 105 and power splitters 106. The coaxial network100 is designed to connect set-top terminals (STTs) 110 a-n within thepremises to the CATV communications system. In the coaxial network, theSTTs 110 a-n (or other devices connected to the network 100) shouldpreferably be able to communicate with each other. However, there ishigh loss between the STTs 110 a-n due to port-port isolation of thesplitters 106. To reduce the loss between the STTs 110 a-n, a reflector120 is inserted between the coaxial network 100 and the CATVcommunications system. The reflector 120 contains one or moreband-reject filters that are centered on frequencies used to communicatebetween the STTs 110 a-n. The filters reflect signals at thesefrequencies with low loss, so that the loss between STTs is minimized.Additionally, the band reject filters prevent the in-home signals fromentering the CATV communications system. It will be appreciated that theblock diagram of FIG. 1 can be reconfigured into several differentconfigurations. For example, the splitters 106 can be incorporated intothe reflector 120. Additionally, the reflector 120 shown operates usingreflection of the signals, but other techniques could be used to reduceloss in the desired frequency bands. For example, it is possible todesign a splitter that has reduced isolation in particular frequencybands, particularly in the modem's low band and high band. If thismethod were used, it would still be desirable to keep the coaxialnetwork signals from leaking into the communications system. To reducethis leakage, an amplifier having sufficient reverse isolation could beplaced in line with the cable from the communications system to thecoaxial network. Further information regarding the reflector 120 can befound in copending U.S. patent application Ser. No. 10/342,670 filedJan. 15, 2003, the disclosure and teachings of which are herebyincorporated by reference.

FIG. 2 illustrates a block diagram of two networked modems 205, 210 anda frequency range plan 215 that are suitable for employing the fullduplex wideband communications in accordance with the present invention.Two modems 205, 210 are shown connected to the coaxial network 100.Specifically, the modems 205, 210 communicate with each other, or othermodems. In accordance with the present invention, the modems 205, 210communicate in full duplex wideband mode. That is to say that modem A205 may transmit signals in a low band 216 and modem B 210 may transmitin a high band 217 with each other. As will be discussed further below,the channel allocated to the modems 205, 210 may change. Only two modems205, 210 are shown in this illustration; however, since several modemsmay be operating simultaneously in the coaxial network 100, there arepreferably multiple wideband channels in bands 216 and 217 in thefrequency range 215 to avoid conflict. Other signals transmitted in thefrequency range 215 comprise a reverse band 218 from, for example, 5 MHzto 40 MHz that the STTs 110 use to communicate back to the headendfacility in the system. Additionally, a forward band 219, ranging from50 MHz to 870 MHz, carries several channels of downstream programs thatare broadcasted from the headend facility to the STTs 110 throughout thesystem.

The modems 205, 210 each include a wideband modem 220, 222 comprisingtransmitters 225, 226 and receivers 227, 228 for high data ratecommunications, such as transmitting and receiving stored videopresentations, within the coaxial network 100. The preferred modulationmethod for the wideband data communications is QAM (quadrature amplitudemodulation), and typically the frequencies are above the forward band219. The wideband modems 220, 222 also include a band-select switch 230,232 and a duplexer 234, 236 for routing the wideband signals.

A medium access method is similar to frequency division multiple accesswith frequency division duplex (FDMA/FDD). FDMA/FDD is appropriate forsystems having a base station and multiple users, such as cellulartelephone. In the FDMA/FDD system, the base station transmits in adownlink band, and the users transmit in an uplink band. The receiver isisolated from the transmitter by a duplexer. In accordance with thepresent invention, however, coupled modems 205, 210, or STTs thatinclude modems 205, 210, communicate directly with each other (e.g.,from STT 110 a to STT n) rather than the conventional method. In otherwords, there is no base station in the coaxial network 100. To allow anytwo wideband modems 205, 210 to communicate in this manner, however, theFDD scheme is no longer sufficient.

To allow the wideband modems 205, 210 to communicate in accordance withthe present invention, the modems 205, 210 can transmit and receive ineither of two bands (e.g., low band 216 and high band 217). Theelectronically-controlled band select switch 230, 232 allows reversingthe connection of the transmitter 225, 226 and receiver 227, 228 to theduplexer 234, 236. As shown in FIG. 2, modem A 205 is set to transmit inthe low band 216 and receive in the high band 217, and modem B 210 isset to transmit in the high band 217 and receive in the low band 216.Transmitting and receiving in a frequency included in either the highband or the low band can be optimized and is discussed further below.For either setting of the band select switch 230, 232, the duplexer 234,236 attenuates the transmit signal so that the receiver sensitivity isnot degraded by the transmitter (i.e., modem A's transmitter 225 doesnot affect modem A's receiver 227). Each band 216, 217 may containmultiple signals to allow multiple pairs of modems to communicatesimultaneously. The transmitters 225, 226 and receivers 227, 228 need tobe able to function over a frequency range that includes both the highand low bands. The switch 230, 232 should preferably be a monolithicdouble-pole double-throw type. The duplexer 234, 236 should preferablyuse dielectric resonator technology, while the control channel diplexer255, 257 is preferably an LC filter.

The modems 205, 210 also include a control modem 237, 238 comprisingtransmitters 240, 242 and receivers 245, 247 used for controlcommunications among the modems 205, 210 within the coaxial network 100.More specifically, the control transmitter 240, 242 provides controlinformation, such as an optimized transmitting frequency of the widebandmodem, or requests, such as a request for a stored video presentation,to at least one control receiver 245, 247. The control receiver 245, 247then receives the information or request and acts accordingly.

In contrast to the full duplex wideband modems 220, 222, the controlmodems 237, 238 operate on a single frequency and in half duplex mode.Additionally, the single frequency is separate from bands 216, 217 usedby the wideband modems 220, 222. The control frequency 250 used by thecontrol modem 237, 238 is typically below the reverse band 218, forexample, at 4.5 MHz. The control signals and the wideband datacommunications signals are routed to the coaxial network 100 using thecontrol channel diplexer 255, 257.

The control modems 237, 238 send and receive data packets as burstpackages using a modulation scheme such as FSK (frequency shift keying).Each packet includes an error-detection code and a destination address.The control modems 237, 238 use a random access protocol similar toALOHA in a known manner. A protocol for control communications from, forexample, modem A 237 to modem B 238 may be summarized as follows:

Modem A 237 sends a packet to modem B 238 and then waits foracknowledgement;

assuming modem B 238 receives the packet with no errors and the addressis that of modem B 238, modem B 238 sends a short acknowledgement;

if the acknowledgement signal is received by modem A 237, then modem A237 sends the next packet. If the acknowledgement signal is not receivedwithin a specified time, modem A 237 waits a random time and resends theinitial packet.

FIG. 3 illustrates a simplified block diagram of a radio frequency (RF)portion of a set-top terminal (STT). STT 300 includes diplexer 305,which isolates tuners 310, 320, 330 from a reverse transmitter 308. Thereverse transmitter 308 transmits signals to the headend facility in thecommunications system. Tuners 310, 320, 330 can be used to receive livetelevision signals (CATV signals), record to a hard drive, or receivecable modem signals. The tuners 310, 320, 330 are capable of receivingQAM signals. Advantageously, a wideband modem 220, 222 that uses some ofthese existing STT functions can be added to the STT 300.

FIG. 4 illustrates a simplified STT including a wideband modem inaccordance with the present invention. CATV signals are received fromthe communications system at diplexer 305. Diplexer 405 provides theCATV signals and any modem RF signals to the intended destinationdepending upon the received signal frequency. In accordance with thepresent invention, tuner 410 can be configured to act as the widebandreceiver 227 shown in FIG. 2, and switch 415 is added to select theappropriate signal path depending upon the type of received signals.Accordingly, switch 415 connects the tuner 410 to receive widebandcommunications signals from another modem 210. In the event that the STT400 requires a third tuner to receive CATV signals, the switch 415connects the tuner 410 to the communications system. The STT's reversetransmitter 420 may be shared between the CATV reverse band 218 and thecontrol channel signals 250. The reverse transmitter 420 may beconfigured as an FSK transmitter.

Returning to FIG. 2, a communications protocol needs to be establishedbetween two modems. A simplified example of a protocol used by theinitiating modem 205 and the receiving modem 210 follows assumingknowledge of unused frequencies and that it is arbitrarily chosen thatmodem A 205 transmits in the low band.

Modem A 205 sets the band switch to Tx/Rx=low/high;

modem A 205 chooses from the unused frequencies low and high bandfrequencies (f_(L) and f_(H));

modem A 205 uses the control transmitter 240 to send the chosenfrequency information to modem B 210;

modem B 210 sends an acknowledgement using control transmitter 242 and,based on the frequency chosen by modem A 205, sets the band switch 232to Tx/Rx=high/low and tunes the wideband receiver 228 to the frequencyin the low band (f_(L));

modem A 205 then tunes its wideband receiver 227 to the frequency in thehigh band (f_(H)) and begins transmitting data at f_(L);

modem B 210 begins transmitting at f_(H); and

modem A 205 uses control transmitter 240 to send a message to any othermodems on the network indicating that the two chosen frequencies (f_(L)and f_(H))are currently in use.

Another embodiment of a full duplex communications modem for the coaxialnetwork 100 is a client modem. A client modem includes a widebandreceiver and a control transmitter. The client modem does not include awideband transmitter or control receiver. In this manner, the clientmodem uses the control transmitter to request a wideband transmissionfrom a server wideband modem and then receives the wideband transmissionusing its wideband receiver. A typical application for the client modemis to request and receive video programs stored in an STT that isconnected to or containing the wideband communications modem 205.

As previously discussed, the modem signals are reflected and containedwithin the coaxial network 100 by filters within the reflector 120 (FIG.1). In this manner, the loss between modems is minimized. However,referring to FIG. 1, the signal between modems may take several pathsother than the path to and from the reflector 120. For example, there isa path between modems included in STT 110 a and STT 110 b across thesplitter 130. The multiple signal paths (i.e., multipath environment)cause distortions to the frequency response of the coaxial network 100,which may include deep nulls 505 (FIG. 5).

FIG. 5 is a graph illustrating a frequency response 500 of a coaxialnetwork 100 having a multipath environment. The frequency response 500is within the full duplex wideband communications signal band. Thecontrol modem signal is not very susceptible to multipath distortionsince its bandwidth is small and the modulation method is usually simple(e.g., FSK).

The present invention includes methods to optimize communication betweenwideband modems in a multipath environment. The methods involveoptimizing the QAM signal parameters based on RF center frequency;bandwidth; and QAM constellation. The last two parameters affect themaximum data rate of the channel. When two modems 205, 210 connect forthe first time, a search algorithm can be used to determine the bestsignal parameters for each direction of communication. For example,using an FSK signal in the control channel, modem A 205 can requestmodem B 210 to transmit at a given frequency. Modem A 205 can thenmeasure the signal quality at that frequency. This is repeated atseveral frequencies until the optimal frequency is found. An example ofa possible search sequence is shown in Table 1. Once the optimal signalparameters are found, those parameters are stored by both modems 205,210 so that the search algorithm need not be repeated. Signal quality isdetermined from measurements made by the receiving modem, including oneor more of the following: signal amplitude, constellation SNR (signal tonoise ratio); tap values of the adaptive equalizer, and bit error rate.

TABLE 1 Example of Search Sequence for Optimal Transmit SignalParameters Center Bandwidth Parameter Set Frequency (MHz) ConstellationData Rate 1 873 6 256 Highest 2 874 6 256 Highest 3 875 6 256 Highest 4876 6 256 Highest 5 877 6 256 Highest 6 878 6 256 Highest 7 879 6 256Highest 8 873 6 64 9 874 6 64 10 876 6 64 11 877 6 64 12 878 6 64 13 8796 64 14 879 6 64 15 873 3 256 16 874 3 256 17 875 3 256 18 876 3 256 19877 3 256 20 878 3 256 21 879 3 256 22 873 3 64 Lowest 23 874 3 64Lowest 24 875 3 64 Lowest 25 876 3 64 Lowest 26 877 3 64 Lowest 27 878 364 Lowest 28 879 3 64 Lowest

If there are several modems connected to the coaxial network 100, forexample, one server modem and several client modems, the server modemmay have to transmit to two or more client modems simultaneously.Considering a two-client example, it may happen that, due to multipathdistortion, the frequency responses from server modem 110 a to clientmodems 110 b and 110 d are not similar. In this case, the optimizationof the signal parameters should take both frequency responses intoaccount. On initial connection, each client modem performs the searchalgorithm described hereinabove. An integer quality score based onsignal measurements is assigned to each parameter set of Table 1, with 7equal to the highest quality. Any score above 0 indicates an acceptablequality. The signal parameter table for client modems 110 b and 110 d isstored in the server modem 110 a. Therefore, the server modem 110 a cansort the tables to find the highest scores for each client modem 110b-n. By way of example, the overall score could be calculated as:overall score=min(client 110 b score, client 110 d score). The resultmight appear as shown in Table 2. For this example, parameter set i isoptimal.

TABLE 2 Example of Sorted Signal Quality Scores Score Client ModemClient Modem Overall Parameter Set 110b 110d Score Data Rate i 4 3 3Medium j 6 3 3 Lowest k 5 2 2 Medium m 0 2 0 Highest n 2 0 0 HighestEtc. Etc. Etc. Etc. Etc.

It should be emphasized that the above-described embodiments of theinvention are merely possible examples, among others, of theimplementations, setting forth a clear understanding of the principlesof the invention. Many variations and modifications may be made to theabove-described embodiments of the invention without departingsubstantially from the principles of the invention. All suchmodifications and variations are intended to be included herein withinthe scope of the disclosure and invention and protected by the followingclaims. In addition, the scope of the invention includes embodying thefunctionality of the preferred embodiments of the invention in logicembodied in hardware and/or software-configured mediums.

1. A full duplex wideband modem, comprising: a wideband transmitter fortransmitting high data rate communications; a wideband receiver forreceiving high data rate communications; a band select switch coupled tothe transmitter and receiver for selecting one of a high band or a lowband in accordance with a first unused frequency associated withtransmitted high data rate communications and selecting a second unusedfrequency in the unselected high band or low band associated withreceived high data rate communications, wherein the band select switchpasses both the transmitted high data rate communications and thereceived high data rate communications, a duplexer for isolating thewideband receiver from the wideband transmitter, wherein the band selectswitch reverses the connection of the wideband transmitter and thewideband receiver to a high-pass and a low-pass port of the duplexer,wherein the duplexer attenuates the transmitted high data ratecommunications, and wherein the full duplex wideband modem communicateswith a second full duplex wideband modem when the band select switch ofeach full duplex wideband modem is set in opposite positions.
 2. Thefull duplex wideband modem of claim 1, further comprising: a controltransmitter for sending control information to at least one coupled fullduplex wideband modem, wherein the control information includes thefirst unused frequency and the second unused frequency of at least oneconnected full duplex wideband modem, wherein the control informationinstructs one of the at least one coupled full duplex wideband modem toreceive the high data rate communications in the first unused frequencyand transmit the high data rate communications in the second unusedfrequency and informs the remaining coupled full duplex wideband modemsthat the first and second unused frequencies are no longer unused; and acontrol receiver for receiving control information from the at least onecoupled full duplex wideband modem.
 3. The full duplex wideband modem ofclaim 2, wherein a high frequency band includes a plurality offrequencies in which to transmit and receive the high data ratecommunications, and wherein a low frequency band includes a plurality offrequencies in which to transmit and receive the high data ratecommunications, wherein the used frequencies are currently in use byother coupled full duplex wideband modems.
 4. The full duplex widebandmodem of claim 1, wherein the high data rate communications is a videopresentation.
 5. A coaxial network for communicating high data ratesignals, the coaxial network comprising a plurality of wideband modemsfor transmitting and receiving high data rate communications between twoor more of the plurality of modems in the coaxial network, a widebandmodem comprising: a transmitter for transmitting the high data ratecommunications; a receiver for receiving the high data ratecommunications; and a band select switch coupled to the transmitter andreceiver for selecting one of a high band or a low band in accordancewith a first unused frequency associated with transmitted high data ratecommunications and a second unused frequency associated with receivedhigh data rate communications, wherein the band select switch passesboth the transmitted high data rate communications and the received highdata rate communications, a duplexer for isolating the wideband receiverfrom the wideband transmitter, wherein the band select switch reversesthe connection of the wideband transmitter and the wideband receiver toa high-pass and a low-pass port of the duplexer, wherein the duplexerattenuates the transmitted high data rate communications, and whereinthe band select switch of one of the plurality of wideband modems and aband select switch of a second of the plurality of wideband modemscommunicate with each other when the band select switches are set inopposite positions.
 6. The coaxial network of claim 5, wherein the highdata rate communications include a video presentation.
 7. The coaxialnetwork of claim 5, wherein the duplexer is coupled to the band selectswitch for receiving and providing the transmitted high data ratecommunications to the coaxial network, and for receiving and providingthe received high data rate communications to the band select switch,wherein the high data rate communications are isolated from othersignals by a high pass filter.
 8. The coaxial network of claim 7, thewideband modem further comprising a control modem for providinginformation regarding the first unused frequency associated with thetransmitted high data rate communications and the second unusedfrequency associated with the received high data rate communications. 9.The coaxial network of claim 8, wherein the control modem comprises: acontrol transmitter for providing the information to the plurality ofwideband modems; and a control receiver for receiving information fromthe plurality of wideband modems.
 10. The coaxial network of claim 9,wherein a high frequency band includes a plurality of frequencies inwhich to transmit and receive the high data rate communications, andwherein a low frequency band includes a plurality of frequencies inwhich to transmit and receive the high data rate communications, whereinthe selected first and second unused frequencies become used frequenciesto the other plurality of wideband modems for selection.
 11. The coaxialnetwork of claim 5, wherein the wideband modem determines the first andsecond unused frequencies by requesting at least one other communicatingmodem to transmit a return signal at a particular unused frequency andanalyzing the quality of the return signal.
 12. The coaxial network ofclaim 11, wherein the quality of the return signal from the at least oneother communicating modem is determined by at least one of an amplitude,signal to noise ratio, and bit error rate of the return signal.
 13. Thecoaxial network of claim 11, wherein the wideband modem requests thereturn signal from the at least one other communicating modem using FSKcommunications.
 14. The coaxial network of claim 11, wherein thewideband modem continues to request the at least one other communicatingmodem to transmit a return signal at numerous unused frequencies untilan optimized first and second available frequency is determined.